1. Field of the Invention
The present invention relates to bicycle gear shift control systems, and more particularly, to a bicycle gear shift control system capable of avoiding frequent gear shifting.
2. Description of Related Art
A conventional bicycle capable of performing automatic gear shift control typically comprises a microcomputer configured with a gear shifting logic, such that the microcomputer controls a corresponding derailleur to perform gear shifting whenever a gear shift control criterion of the gear shifting logic is met, for example, when the speed of the conventional bicycle reaches a predetermined speed. The cyclist who is pedaling the conventional bicycle perceives a change in a pedaling frequency and a pedaling load because the gear shifting action has changed the gear ratio.
However, cycling never takes place in an invariable environment. For example, cyclists not only stop for a red traffic light, but make different abrupt changes to the cycling speed in order to ride up or ride down a ramp. Still, the microcomputer responds to any large abrupt change in cycling speed by performing automatic gear shift control in accordance with its gear shifting logic. As a result, frequent gear shifting poses an issue. If completion of gear shift control is always immediately followed by detection that a gear shift control criterion has just been met, gear shift control will have to be performed repeatedly. The cyclists perceive persistent variation of a pedaling frequency and a pedaling load and thus feel uncomfortable and frustrated. Also, if a gear-up operation is immediately followed by a gear-down operation due to a change in cycling speed, the cyclists will perceive reciprocating gear shift movement despite the unchanged cycling speed; as a result, the cyclists perceive persistent variation of a pedaling frequency and a pedaling load and thus feel uncomfortable and frustrated.
Sometimes a cyclist prefers manual gear shifting over ongoing automatic gear shift control while cycling. To meet the aforesaid need, the prior art allows the cyclist to switch the microcomputer between an automatic gear shifting mode and a manual gear shifting mode. In the manual gear shifting mode, the cyclist performs gear shifting manually. In the automatic gear shifting mode, it is the microcomputer rather than the cyclist that determines and operates gear shifting.
Nonetheless, the aforesaid prior art has a drawback. Sometimes a cyclist wants to downshift manually for just a short period of time in the automatic gear shifting mode in order to ride up a short ramp or attempt quick overtaking, for example. To this end, the cyclist has to switch to the manual gear shifting mode before down shifting, because it is impossible to perform gear shifting in automatic gear shifting mode. However, it is inconvenient for the cyclist to do so.